The companies responsible for running Croydon’s tram network were ignorant of the risks posed by trams overturning, an eventuality they did not see as “credible”, according to investigators.

Simon French, the chief inspector of rail accidents at the Rail Accident Investigation Branch (RAIB), told the Advertiser there was not sufficient understanding of the risk among tram management that a tram might overturn if it approached a bend at too high a speed.

Croydon Tramlink is operated by Tram Operations Limited (TOL), a company run by FirstGroup under contract to Transport for London (TfL), who also have some managerial oversight of the system.

He said: “The incident on the 31st was very serious and our detailed analysis has identified that in fact it got very close to the point of overturning. For that to have led to actions to avoid the accident on November 9 required two things.

“Firstly it required the application of the hazard brake on the approach to the corner to have been reported. Therefore you need a ‘just culture’ where people feel able to report mistakes of that kind.

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He added: “It hadn’t been seen as credible that a tram could approach a corner so fast it would overturn.

“So it certainly was a precursor event, for it to have to led to action would have required a higher awareness of risk and that’s why we’ve urged work to be done in this area and for proper guidance to be provided to all tramway operators and designers on potential hazards on how the risk should be mitigated.”

A map showing where the crash happened (Image: RAIB)

The RAIB report into the causes of the crash, which was released today (Thursday, December 7) shows more damning evidence that the management of those two bodies should have been aware of the potential risk of a tram overturning.

It points to five cases over the past three decades around the world where trams have overturned.

In 1993, in Poznan, Poland, five people were killed and more than 60 injured when a tram overturned on a curve.

Three years later, in Kamianske, Ukraine, 34 people were killed and more than 100 injured when a runaway tram crashed into a wall due to a brake failure.

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Then, in 2011, a historic tram derailed on a curve in Rio de Janeiro, causing five deaths and at least 27 injuries.

In 2013, 77 people were injured in Yuen Long, Hong Kong, when a tram tipped after going too fast around a bend, but was prevented from fully turning over by a mast.

The other incident happened in Dusseldorf, Germany, in 2014, when several people were injured after a tram derailed at a junction.

A section from the RAIB report on other incidents where trams overturned (Image: RAIB)

Despite these incidents, the RAIB said TOL and TfL’s route hazard assessments “did not take account of evidence showing the level of risk associated with a tram overturning”

“Although no second generation trams had overturned in the UK, the risk of overturning was apparent from events on tram systems in other parts of the world, historic events on UK tramways and main line rail experience in the UK and overseas,” the report said.

The RAIB also pointed to historic incidents in the UK where old-style double-decker trams tipped over, and UK Highways data showing buses and coaches overturning as well as accidents where trains had overturned.

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“The historic events demonstrate that overturning is an issue which should be considered when assessing risks associated with tram operation,” the report concluded.

In a statement, TfL said it was reviewing and revising risk assessments, alongside First Group, to ensure all scenarios are adequately planned for.

Tim O'Toole, First Group chief executive, said: “We have learned from the RAIB’s analysis and our own internal reviews and we will continue working hard, alongside TfL, to follow the RAIB’s advice and to make further changes where necessary.”